Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Payables and Accruals [Abstract]
Salaries and wages	$ 89,163	$ 82,900
Airport obligations	80,134	52,029
Federal excise and other passenger taxes and fees payable	65,312	60,604
Aircraft maintenance	38,099	59,805
Fuel	28,510	25,368
Aircraft and facility lease obligations	20,656	15,149
Interest payable	16,941	18,086
Other	34,706	25,736
Other current liabilities	$ 373,521	$ 339,677